The present invention relates to an internal combustion engine control apparatus and in particular to an internal combustion engine control apparatus for controlling the internal combustion engine based upon the output of a hot wire air flow meter.
Internal combustion engine control apparatus which detect an intake air quantity fed to the engine for calculating various engine controlled quantities based upon the detected intake air quantity have heretofore been known. Many of such internal combustion engine control apparatus use a hot wire air flow meter for detecting the intake air quantity. This type of air flow meter has a current heating element in an air intake passage. A current conducting through the element is controlled so that the element is heated to a predetermined temperature or so that it provides a predetermined quantity of heat. Since the heat radiated from the current heating element corresponds to the intake air quantity, the intake air quantity can be detected from the conducting current or the temperature of the heating element. This type of air flow meter has advantages in that it has a fast response, a wide dynamic range and a high precision and is compact in size and economical.
However, a large current is conducted through such a hot wire air flow meter until the current heated element is heated to a predetermined temperature (for example, the temperature of the intake air plus 200.degree. C.)(this will be referred to as "activated or activation"). Accordingly, the intake air quantity detected by the hot wire air flow meter becomes remarkably higher than the actual value. If the engine is started by the activation of the hot wire air flow meter, accurate control can not be made. For example, if the fuel quantity is controlled by directly using the detection result, the air/fuel ratio becomes a remarkably fuel rich ratio.
Therefore, a method of controlling the fuel injection quantity of a predetermined value until a predetermined period of time which is longer than the period of time taken to activate the hot wire air flow meter after turning on of a key switch is proposed in Japanese Unexamined Patent Publication Sho 57-173537 and a method of controlling the fuel injection quantity based upon control factors such as coolant temperature other than intake air quantity is proposed in U.S. Pat. No. 4,564,907.
In these internal engine control apparatus, so-called smoothing processing in which previously executed controlled quantities and newly calculated controlled quantities are averaged at a given factor is performed and the engine is controlled based upon the controlled quantity which is subjected to the smoothing processing. Therefore, control is not immediately made based upon the intake air quantity even after the lapse of the predetermined period of time and the activation of the air flow meter for the reason as follows: The internal combustion engine control apparatus calculates a controlled quantity having an error based on no intake air quantity until the predetermined period of time has lapsed. The controlled quantity after the lapse of the predetermined period of time is influenced by the controlled quantity having an error due to the smoothing processing.
Therefore, the fuel injection quantity may continue to be excessive with respect to the actual intake air quantity for a while even after the activation of the hot wire air flow meter. In this case, the air/fuel ratio is a fuel rich ratio for a while, resulting in that the emission and fuel consumption is worsened.
In the system of the above mentioned U.S. Pat. No. 4,564,907, fuel is supplied at a constant rate corresponding to the engine coolant temperature if the fuel injection quantity can not be operated from the output of the hot wire air flow meter, that is, for a predetermined period of time after turning on of a key switch. Thereafter, the fuel injection quantity is operated from the intake air quantity detected by the hot wire air flow meter and the engine rotation number. Briefly, the period of time which is taken to heat the hot wire of the air flow meter to a predetermined temperature is preliminarily predicted and preset.
However, if starting of the internal combustion engine is completed within the preset time which is taken to heat the hot wire of the air flow meter in this system, the fuel quantity corresponding to the engine coolant temperature is injected also after the completion of the engine starting, resulting in a poor controllability. If starting of the engine is not completed within the preset period of time for heating the hot wire of the air flow meter, the fuel injection is operated based upon the erroneous output value of the hot wire air flow meter on completion of starting of the engine, resulting in problems such as worsened emission, poor drivability and engine stall.